How is this not being allowed?
Many site issues can be caused by corrupt cookies or cache.
'''Warning ! ! ''' This will log you out of sites you're
logged in to. You may also lose any settings
for that website.
* [https://support.mozilla.org/en-US/kb/delete-cookies-remove-info-websites-stored Delete cookies to remove the information websites have stored on your computer] {web link}
* [https://support.mozilla.org/en-US/kb/how-clear-firefox-cache How to clear the Firefox cache] {web link}
If there is still a problem, '''[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Start Firefox in Safe Mode]''' {web link}
by holding down the '''<Shift> ''(Mac=Options)''''' key, and then starting Firefox.
A small dialog should appear. Click '''Start In Safe Mode''' (not Refresh).
Did this help?
While you are in safe mode;
Try disabling graphics hardware acceleration in Firefox. Since this feature was added to Firefox it has gradually improved but there are still a few glitches.
''[https://support.mozilla.org/en-US/kb/forum-response-disable-hardware-acceleration How to disable Hardware Acceleration]'' {web link}

Thank you Fred McD. I have solved the problem finally by choosing Firefox in "Safe mode".
Best regards,
Bosjehout

Then you got problems if it works in "Safe Mode". This means something installed isn't the cause of the problem addons/extensions or security software caused.

''bosjehout [[#answer-1208448|said]]''
<blockquote>
Thank you Fred McD. I have solved the problem finally by choosing Firefox in "Safe mode".
Best regards,
Bosjehout
</blockquote>
Then you got problems if it works in "Safe Mode". This means something installed isn't the cause of the problem addons/extensions or security software caused.

In the Add-ons Manager, on the left, select Extensions.
Disable a few add-ons, then Restart Firefox.

Some added toolbar and anti-virus add-ons are known to
cause Firefox issues. Disable All Of them.

If the problem continues, disable some more (restarting
FF). Continue until the problem is gone. After, you know
what group is causing the issue.
Re-enable the last group ONE AT A TIME (restarting FF)
until the problem returns.

Once you think you found the problem, disable that and
re-enable all the others, then restart again. Let us know
who the suspect is, detective.

It could be the work of one of your add-ons,
or it could be '''Hardware Acceleration. '''
''[https://support.mozilla.org/en-US/kb/forum-response-disable-hardware-acceleration How to disable Hardware Acceleration]'' {web link}
Type '''about:addons'''<enter> in the address bar to open
your Add-ons Manager. Hot key;
'''<Control> ''(Mac=<Command>)'' <Shift> A) '''
In the Add-ons Manager, on the left, select '''Extensions. '''
Disable a few add-ons, then '''Restart Firefox. '''
Some added toolbar and anti-virus add-ons are known to
cause Firefox issues. '''Disable All Of them. '''
If the problem continues, disable some more (restarting
FF). Continue until the problem is gone. After, you know
what group is causing the issue.
Re-enable the last group '''ONE AT A TIME''' (restarting FF)
until the problem returns.
Once you think you found the problem, disable that and
re-enable all the others, then restart again. Let us know
who the suspect is, detective.

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block (wanted) content (Adblock Plus, NoScript, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block (wanted) content.
*make sure your extensions and filters are updated to the latest version
*https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems
Firefox shows the shield icon at the left end of the location/address bar in case Content Blocking is blocking content.
*click the shield icon for more detail and possibly disable the protection
You can check the Web Console about what content is blocked
*"3-bar" menu button or Tools -> Web Developer
*https://support.mozilla.org/en-US/kb/tracking-protection
*https://support.mozilla.org/en-US/kb/content-blocking